The invention relates to the manipulation of carriers (also called boards or substrates) of printing circuits, and more particularly to improvements in methods of and in apparatus for aligning or orienting printed circuit carriers in screen printing, photoprinting and other machines for the application of printed circuits so that each of a short or long series of carriers is moved to a predetermined position for the application of a printed circuit thereto.
It is important to position the printed circuit carriers with a very high degree of accuracy prior to the application of printed circuits. This holds true regardless of whether the machine which applies printing circuits is a screen printing, an optical printing or any other machine. More specifically, the carriers must be positioned with a high degree of accuracy with respect to the printing unit which applies printed matter to a properly positioned carrier.
Commonly owned U.S. Pat. No. 4,700,488 granted Oct. 20, 1987 for "Arrangement for aligning a printed circuit substrate in a printing machine" discloses machine wherein the carriers or substrates to be provided with printed circuits are formed with pairs of indicia in the form of locating holes. These holes receive locating pins which are mounted on so-called aligning or fixing devices. In order to compensate for eventual deviations of the shape and/or size and/or position of one or more locating holes from an optimum shape, size and/or position, the patented machine comprises expandible and contractible locating pins. Deviations from an optimum position, shape and/or size of a locating hole can develop as a result of manufacturing tolerances, as a result of temperature-induced expansion or contraction of a portion of or the entire carrier and/or for a number of other reasons. The locating pins of the patented machine are contracted prior to introduction into the holes of a carrier, and the locating pins are thereupon caused to expand so as to engage the surfaces bounding the respective holes. The diameter of each locating pin in contracted condition is smaller or even much smaller than the diameter of a hole so that a contracted locating pin can be readily inserted into the hole of a carrier to be thereupon expanded into firm engagement with the surface around the hole.
Since the complexity of printed circuits is on the increase, with simultaneous reduction of the width of electric conductors, accurate positioning of a printed circuit carrier in a screen printing or optical printing machine becomes even more important. Thus, even slight deviations from an optimum position of the carrier with reference to the circuit applying unit is likely to result in non-application of one or more marginal portions of the circuit so that the imprinted carrier must be discarded.